A fusion reactor blanket has to withstand harsh conditions such as 14 MeV high-energy neutron radiation of the reactor core and impact of high-energy density heat flow (>1 MW/m2). The reduced activation ferritic/martensitic (RAFM) steel, which has the merits such as resistance to high-energy neutron radiation, low activation, good performances at a high temperature, is considered as the preferred structural material for the first fusion reactor in the future. China low activation martensitic (CLAM) steel is a kind of RAFM steel, which is developed by Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences with wide collaboration, obtaining an independent intellectual property right. After being developed for more than ten years, the CLAM steel has been chosen as the preferred structural material of China ITER test blanket module, and is also the preferred structural material of China Fusion Engineering Test Reactor Blanket. In addition, as the environment where the fusion reactor blanket is located is extreme, the blanket structure should be cooled by delivering a lot of coolant into the interior thereof, therefore the blanket structure is also quite complex. The gas protective welding (e.g. Tungsten Inert Gas (TIG) welding and Metal Inert Gas Arc (MIG) Welding) currently has been widely used in the process of welding the blanket structure as it has good welding adaptability.
The chemical components of the CLAM steel are shown in Table 1.
According to formulas (1) and (2), the CLAM steel has the Cr equivalent weight of 11.8 and the Ni equivalent weight of 3.2 by calculation.Cr equivalent weight: Creq=Cr+6Si+V+5Nb+2.5Ta+1.5W  (1)Ni equivalent weight: Nieq=Ni+Co+0.3Cu+0.5Mn+25N+30C  (2)
It can be seen from the Schaeffler-Schneier FIGURE (see FIG. 1) that the CLAM steel has a strong tendency of forming ferrites during the solidification process, and many blocky δ ferrites will exist in the joint if the base material of the CLAM steel is taken as the welding filler material. It is found from research that the generation of the blocky ferrites reduces the strength of welding lines, seriously weakens the impact resistance of the joint, and it will increase the tendency of crystallization cracking and reduce the high-temperature creeping performance, etc. It is proper to say that the existence of the blocky δ ferrites is the fundamental cause to deterioration of the performances of the joint. Therefore, the key technology for improving the performances of the joint is related to how to reduce and even eliminate the δ ferrites in the welding structure. The present invention designs and optimizes the chemical compositions of the welding wire of the CLAM steel through analysis of influence of the elementary compositions on the formation of ferrites.
TABLE 1Designed Compositions of the CLAM Steel (wt %)ElementCCrWVTaMnSiPSContent0.08~0.128.5~9.51.3~1.70.15~0.250.12~0.180.45~0.55<0.05<0.005<0.005ElementNONiCuAlCoAgMoNbContent<0.02<0.01<0.01<0.01<0.01<0.01<0.005<0.005<0.005